[lib][native] Introduce NeynarClientProvider

Summary:
This lets us share a single Neynar client across the whole component tree.

Depends on D11388

Test Plan: Tested this using my own FID by hooking it into FarcasterDataHandler in a later commit

Reviewers: atul, ginsu

Reviewed By: ginsu

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D11389